1. Field of the Invention
The present invention relates to a profile control apparatus for a thermal working machine, and more specifically to a profile control apparatus incorporated with an NC system for a thermal cutting machine.
2. Description of the Prior Art
In thermal working machines such as a laser or gas cutting machine, a flat workpiece mounted on a table is cut off by a working head kept at a predetermined height over the workpiece. In general, however, since there inevitably exists a warp in a flat workpiece, a profile control apparatus is required to maintain the working head at a predetermined distance away from the surface of a non-flat workpiece. This is because the laser beam should always be condensed (focused) at the middle of the thickness of the workpiece having a warp, for instance.
Conventionally, however, the profile control apparatus has been provided independently from an NC system which controls workpiece positions and a working head position. In the conventional profile control apparatus, the working head is so controlled as to be maintained at a predetermined constant distance away from a non-flat workpiece in response to an analog sensor signal indicative of an actual distance between the head and the workpiece.
On the other hand, in the thermal working machines provided with an NC system, a manual pulse generator is usually provided for manually moving the working head along the Z axis by a desired distance. In addition, a pulse signal processor is also incorporated with the NC system in order to drive the head along the Z-axis in response to a pulse signal generated from the manual pulse generator according to the rotational speed of a knob disposed in the manual pulse generator.
In the conventional thermal working machines, since the profile control apparatus is provided independently from the NC system and therefore the working head is controllably driven by the NC system and the profile control apparatus, independently, there exists a problem in that the head drive mechanism is relatively complicated and therefore costly.
Further, where a profile control apparatus is additionally installed on an already-completed thermal working machine provided with an NC system, since the NC system should inevitably be modified, there exists another problem in that a relatively great labor is required and therefore the cost required for the modification is high.